1. Field of the Invention
This invention relates to a double wrap brake band and its manufacturing method for use in an automatic transmission for an automobile.
2. Description of the Related Art
Generally, a construction shown by 200 in FIG. 17 and FIG. 18, for example, has been known as a double wrap brake band for use in an automatic transmission (U.S. Pat. No. 2,867,898). In this structure, the brake band 200 is disposed on an outer peripheral part of a drum 202 concentric with a drive shaft 201 extending from a torque converter not shown.
The double wrap brake band 200 is provided with three bands 210, 211 and 212 formed approximately into annular shape, and friction facings 213, 214 and 215 fastened to the inner peripheral surfaces of the bands 210, 211 and 212. A connecting member 216 connects the circumferential ends of the outside bands 210 and 212 with another circumferential end of the intermediate band 211. A first bracket member 217 is secured to the circumferential ends of the outside bands 210 and 212. A second bracket member 218 is secured to one circumferential end of the intermediate band 211. The first bracket member 217 has an edge for receiving a piston 219 and the second bracket member 218 has an edge for receiving an anchor pin 220.
In the structure shown in FIG. 17 and FIG. 18, the connecting member 216 and the first and second bracket members 217 and 218 are all made of forging segments which are welded to the thick metal straps and then formed into prescribed shapes by broaching. Internal stresses are produced during manufacturing and cause drags between the completed bands 210, 211 and 212 and a drum 202.
To solve the above-mentioned troubles, a structure and its manufacturing method, wherein the connecting member and the first and second bracket members are integrally made of sheet metal and welded to straps made of sheet metal, have been proposed in U.S. patent application Ser. No. 310,340 and have been disclosed in Japan (Japanese Patent Publication No. 58-68523).
However, this structure is apt to distort by heat during manufacturing because the connecting member and the first and the second bracket members are welded to the bands. Further, even the narrow second bracket member, which is secured to the intermediate band, is made of thin sheet metal, so that sufficient strength is not obtainable.
Furthermore, because this structure includes the process in which the connecting member and the first and second bracket members are manufactured from a unit segment, it is difficult to change thicknesses and materials of respective components.
An object of this invention is to solve the above-mentioned troubles.